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ci: speed up submodule update by resolving tips via ls-remote #198

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ci: speed up submodule update by resolving tips via ls-remote #198

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29 changes: 19 additions & 10 deletions .github/workflows/update-submodules.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -17,9 +17,13 @@ jobs:
uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
with:
ref: main
submodules: recursive
# Submodule contents are NOT needed: we only resolve each submodule's
# latest branch tip via `git ls-remote` and update the gitlink in the
# index. Cloning the (large) submodules would dominate the runtime.
submodules: false
token: ${{ secrets.EURO_OFFICE_MIRROR_TOKEN }}
fetch-depth: 0
# A shallow checkout is enough to create the PR branch.
fetch-depth: 1

- name: Configure git identity
run: |
Expand All @@ -44,16 +48,21 @@ jobs:

for path in "${!BRANCHES[@]}"; do
branch="${BRANCHES[$path]}"
if [ ! -d "$path" ]; then
echo "Skipping $path — directory not found"
url="$(git config -f .gitmodules --get "submodule.$path.url" || true)"
if [ -z "$url" ]; then
echo "Skipping $path — not declared in .gitmodules"
continue
fi
echo "Updating $path → $branch"
pushd "$path" > /dev/null
git fetch origin
git checkout "$branch"
git reset --hard "origin/$branch"
popd > /dev/null
# Resolve the branch tip without cloning the submodule.
# Auth is provided by the credentials checkout persisted for github.com.
sha="$(git ls-remote "$url" "refs/heads/$branch" | awk '{print $1}')"
if [ -z "$sha" ]; then
echo "Skipping $path — no '$branch' branch on $url"
continue
fi
echo "Updating $path → $branch ($sha)"
# Update the gitlink directly in the index — no working-tree checkout needed.
git update-index --cacheinfo "160000,$sha,$path"
done

- name: Open PR if submodule pointers changed
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